At the 5 August SBMS
Meeting we will be Planning for the up coming contest.. The SBMS
meets at the American Legion Hall 1024 Main Street (south of the 91
freeway) in Corona, CA at 1900 hours local time on the first Thursday
of each month. Check out the SBMS web site at
http://www.ham-radio.com/sbms/.

SBMS meeting parking- We have become a great number of members at
meetings. We park next to the church in the adjacent lot or on the
street and or in the lot across the street. Across the street the
sign on the building shows: 1025 Main Street. MAIN STREET BISTRO. The
sign on the parking lot says: CLIN CHIROPRACTIC CARE Dick, WB6DNX

A reminder that the third Saturday of each month is Microwave
Activity Day starting after the Pomona/ Cal Poly Swap meet through
mid afternoon.

Last meeting_ Chip, N6CA
had a computer power point presentation about the basic transverter
with reference to the 10GHz versions he is building for Paul, KH6HME
in Hawaii. Mel, WA6JBD had his 3 versions of transverter to show. Mel
discussed use of the microwave "brick" approach he used in his first
version followed by the NEC synthesizer and step recovery diode
approach he used. Mel's main idea was being modular with reliability
in back up parts and good construction of wire Wayne, KH6WZ
demonstrated his latest 10 GHz rig with FT-817 if radio. Wayne's
approach was to be modular and Velcro doesn't keep things from moving
around cabling. Christopher Best, KB3DXR of Huntsville, AL was our
visitor. Welcome. Doug, K6JEY talked about progress being made o the
Owens Valley Radio Observatory Project with the addition of schools
being able to do experiments with pulses sent from the main site. 26
People present

below: Larry, K6HLH had an indicator for checking to see that his
microwave transmitter was really transmitting. He made it from an old
meter from some instrument that had been scraped and added a
waveguide transition with detector to supply a current indication on
the meter when it was in front of a working transmitter. It would
most likely work on several bands around the WR-90 waveguide
frequency.

Activity reported at the July SBMS meeting were: Chris, N9RIN is
reworking his 10 GHz rig; Mel, WA6JBD is working on his 3rd version
of 10 GHz transverter; Chuck, WA6EXV worked WB6CWN in San Diego from
Ridgecrest with a broken waveguide feed on 10 GHz (see SBMS web page
pix) and is working on his controller; Bill, WA6QYR has been working
on a Mojave TVI problem; Ken, W6DTA worked the VHF contest from DM22
on 900, 1200MHz and 10 GHz; Mike, W6YLZ is working to get his rig
weight down under 55 pounds and has a small 24 v supply to help with
the TWT requirements; Doug, K6JEY was on vacation to Alaska and had a
small keyer and oscillator to show; Dennis, WA6NIA worked the contest
and Field Day on 10 GHz; Pat, N6RMJ found a "new spot" in the Mojave
(the old 10 GHz Gunnplexers site of EXV and QYR) to work the contest
and Field Day, and is now on 3456 MHz; Jeff, KN6VR has a working
tower now; Mike, W6YLZ cleaned his shop; Bob, WA6VHS has a working 10
GHz rig and is working on the Verticon synthesizer; John, KJ6HZ
worked the contest on 6 bands; Kurt, K6RRA worked the contest; Wayne,
KH6WZ worked the contest and Field day on 10 GHz; visitor Chris,
KB3DXR is working on getting his system up; Larry KG6EG worked the
contest; Chip, N6CA got ready for his tech talk; Dick, K6HIJ did some
work on the Owens Valley antenna design; Larry, K6HLH worked 7 bands
during the contest and had a power detector to show; Gary, W6JKVC had
some military interference on 433-435 MHz; and Glenn, KE6HPZ worked
the contest on 11 bands.

2005 Microwave Update Planning

On the Microwave Update 2005 Pat N6RMJ is the leader and Dick,
K6HIJ is the registration person. Initially they are looking at the
Sheridan in Cerritos, CA for the site. Chip, N6CA is setting up the
speaker list and encouraging everyone to use a power point type
presentation for his or her material. Chip will also take care of the
proceedings being published. The operation needs a list of surplus
electronic hardware places to visit on Thursday tour. The list needs
to include where the store is located and hours of operation and what
types of materials are available. Bill, WA6QYR is collecting the list
of stores. Judy, KC6UTF has volunteered to help with the XYL/ Spouse
tours. This will be also the 50th anniversary of the SBMS so we are
looking for materials on the first few years of operation to present.
The Dates will be 27-28-29 October 2005.

Where is the info on your favorite surplus or shopping spot for
electronic goodies? Forward that to bburns@ridgenet.net yet.

New inputs on stores to visit during MUD 2005-

OK, I figured that everyone knew about these places, but I have
not seen anyone post anything on the reflector. Where does everyone
go for "stuff"? I would like to know where people go for microwave
and RF surplus, since I seem to have places for non-RF stuff.

Here is a place someone told me about this morning, it's an online
store:

NOTE: I have not gone to most of these places since the mid-80's
when I was in high school, but they are still around. All these
places have new and surplus electronic items, but not much RF- or
microwave-specific things. However, these places are all excellent
alternatives to Fry's or Radio Shack . . .. Wayne, KH6WZ

Every ham should visit Apex Electronics at San Fernando and
Tuxford Rd in Sun Valley. You can build or repair anything from their
huge electronic surplus inventory. They have RF and waveguide parts.
Just a mile to the south in Burbank is Industrial Metal Supply. They
sell common metals in most shapes for industrial/commercial use, but
also over the counter to you and me. Sheet, extrusion, bar, tube,
rods, etc. They will cut for a small fee. Frank WB6CWN

below: Mel, WA6JBD discussed his various version of 10 GHz
transverter at the July SBMS meeting. On the left is his first rig
that has continued to have modifications made to it so that it was
becoming more reliable and had modules that could be cabled around if
there had been a failure in a section. On the right is the third
version, which is coming along nicely. It has some of the
modifications of the first versions in addition to later thoughts and
changes to make a rig that is still better yet.

Owens Valley Radio Observatory Project.

Doug, K6JEY is the lead contact on the project. Dennis, WA6NIA is
the schedule keeper. Dick, K6HIJ is doing the design on the antenna
package. Chuck, WA6EXV is in charge of the hardware construction for
the radios in the feed structure as well as the structure. The
written project description has been approved by the site manager and
is in the hands of the Cal Tech managers awaiting approval. The
initial plan is to provide 1296 MHz and 10 GHz transverter for the
feed of the 120 ft dish at Big Pine site for education to schools
around the world.

below:Wayne, KH6WZ shows his 10 GHz rig to members at the July
SBMS meeting. His package has a photo shoe to attach it to the tripod
and used a metal box he happened to have that was big enough to hold
all the pieces. The wooden handles on the sides helped control the
pointing when in the field. The dish antenna slips over the feed when
all is on the tripod. His power amplifier is mounted on the upper
edge of the arrangement to keep the heat from the rest of the rig.
Wayne uses power poles for interconnection to batteries under the
tripod. His FT-817 IF radio fits in the middle of the assembly along
with a DSP audio unit to help with the received signal bandwidths.
Modular construction was one of Wayne's points in discussing the
pluses of his set up.

Simple Rectangular to Circular Microwave
Waveguide Transitions

D. A. Bathker K6BLG

Summer 2004

For Richard Kolbly K6HIJ and possibly the SB Microwave Society

It often becomes necessary to connect dominant mode rectangular
cross-section waveguide (wg) to dominant mode circular wg with low
reflection (and wg mode purity). The most common example is to
connect a TE-10 rectangular wg to a TE-11 circular wg to be used for
a feed on a microwave dish. In this case the wg modes have similar
field patterns and a simple solution arises.

A difficult way to do this is to construct a taper of some sort,
usually over a length of a few or several wavelengths, gently
blending the two cross-sections. If either wg is operating near
cutoff, or even towards the low end of the recommended rectangular wg
band, reflections will be large and highly variable with frequency.
This occurs because the taper is being forced to convert the 'input'
guide wavelength (gw) to the 'output' gw (in addition to converting
the impedances and slight field pattern changes). The two gw may
differ greatly and give rise, in the main, to the reflections. Such
gw-changing transitions are called inhomogeneous transitions.

A simple alternative is to first size one (or the other) TE
waveguide to force the guide wavelengths to be equal, throughout. In
the case at hand, generally, the rectangular wg is fixed by standards
(e.g. WR-42, perhaps a preamp input), leaving the circular wg
diameter for the feed as a variable. When the gw is uniform
throughout, the (mini) wg system is called homogeneous.

Then, a simple, single-section, quarter wave (gw)
impedance-and-mode-changing transition (transformer) is all that is
needed for many applications. For very broadband applications as many
as 4-quarter wave sections have been used, with full rectangular wg
bandwidth being accommodated with low reflection (Ref.1). The modest
bandwidth solution is only a quarter wave in length while the
broadband solution is but one wavelength in length, far better than a
typical taper and usually better performing as well.

Let us design a simple single-section quarter wave transformer, to
connect WR-42 to a TE-11 mode wg feed. We adopt 24.192 GHz as the
center frequency

The first principle is to size the circular wg to match the
rectangular wg gw. This means the cutoff wavelengths must be equal.
Once that is done, the TE gw's will track (be equal) with frequency,
any frequency.

The second principle comes to us from old coaxial practice
(coaxial being a homogeneous "wg" given a uniform dielectric constant
throughout). The second principle is the familiar quarter wave
impedance matching section Z' = sqrt (Zin x Zout). This works for
coaxial as we all know, and it works for homogeneous hollow wg's as
well.

Lambda-c (cutoff wl) for TE-10 rectangular 'guide is (lambda-c =
2a) with (a) being the width of the 'guide. Lambda-c for circular
'guide (TE-11 mode) is (lambda-c = 2 Pi r/1.84118...) where Pi is
3.14159..., r is the radius of the circular 'guide and the 1.84118...
well, that's a Bessel Function root; it's just wrapped up in the
physics of the matter and we won't be intimidated by that.

We next set the two cutoff equations to be equal; 2a = 2Pi
r/1.84118. In other words, for any "a" (rectangular wg width), there
is a corresponding "r" (circular, TE11 mode wg radius) that forces
the 'guide cutoff wl equality and hence the 'guide wl tracking
&endash; the homogeneous solution. In the case of WR-42 (a = 0.420
inches) the corresponding circular 'guide radius is 0.246 inches. (Do
the arithmetic). This ensures the wanted behavior and note, the size
of the required circular guide is a bit larger than you may be used
to; here, for WR-42 we must use 0.492 inch diameter.

All we have to do then is to design the intermediate matching
section. Now, the equation for TE-mode impedance* (either rectangular
or circular cross-section) is given by Zo = 2b/a, where b is the
height and a is the width of the rectangular 'guide and b = a = 2r
for the circular TE-11 'guide (!). In other words, for WR-42 (b =
0.420 inches, a = 0.210 inches) Zo = 1.000 (relative) (at any
frequency) and for a circular 'guide of radius 0.246 inches Zo =
2.000 (relative) (at any frequency). This is true for any frequency
in either 'guide.

This is the "secret" of the whole matter of connecting these two
'guides ... the impedance ratio is always two (2), whenever their
cutoff wl (and therefore their tracking 'guide wavelengths) are
equal.

Then by our old coaxial knowledge, the single quarter wave
transformer necessary to connect these two 'guides should have an
impedance of [(sq-rt) ( Zin*Zout)] = 1.414Zo. (sq-rt 2Zo). Knowing
that Zo = 2b/a, for all 3 of these TE 'guides, we can confidently say
2b/a = 1.414, or b/a = 0.7071, then b (the quarter wave section) = sq
rt (0.210 x 0.492) = 0.321 inches and a = b/0.7071 = 0.455 inches.
(Do the arithmetic).

So, to connect the rectangular WR-42 to a circular TE-11 'guide
(of diameter 0.492 inches) one needs a 'simple' short quarter wave
(gw) section of specially machined 'guide, having the dimensions of a
= 0.455 inches by b = 0.321 inches, the corners of which are to be
truncated by the 0.492 inch diameter. Thus, the matching transformer
cross-section is a hybrid of rectangular and circular 'guides but
with specific impedance level (1.414 relative).

The length of the matching transformer must be a quarter wave long
in guide wl at the frequency needed. For 24.192 GHz the TE 'guide wl
(for any and all of the three wg's) is very close to 0.600 inch. A
quarter guide wl is therefore 0.150 inch. Because E-plane steps
dominate in this design (respectively 0.055 and 0.086 inches,
one-sided) with the H-plane steps being so small (each is only 0.018
inch, one-sided) and because E-plane steps introduce a shunt
capacitance (just as in coaxial lines) the final transformer length
needs to be about 95% of the true quarter wave gw, or 0.142 inches.

To preserve mode purity (the TE-11 "output") it is recommended
such "simple" transitions be highly mechanically symmetric (up-down,
and sideways) to a few thousandths of an inch, to prevent
higher-order waveguide modes to be excited, particularly near the
higher end of the (rectangular standard recommended) wg band.
Likewise, the feed itself, with slightly large input diameter needs
to be sensibly symmetric as well.

Note: I have built and used several of such transformers in the
900 and 1200 MHz and 3.7-4.2, 7-8 and 11.7-12.2 GHz bands with good
results. No more long, disappointing tapers for me. You too, I
suggest.

I have tried to clarify this description of a simple-minded
process, which has been found to be not so simple to describe after
all. Anyone with questions, criticisms or comments should contact the
author &endash; K6BLG, Box 23 La Canada, CA, 91012. Good microwaving
Gents.....

Dan A. Bathker K6BLG JPL (Ret.) *Power-Voltage definition to be
exact, but it doesn't matter if we are consistent (and we are).

Ref: IEEE Trans. MTT, Feb. 1967 pp. 128-130

4-Section Homogeneous Transformer WR-430 to WC-504

(2.150 x 4.300 to 5.040 inch diam) 1.7-2.6 GHz VSWR Max = 1.05

(To illustrate a, b, and the corner radii)

below: Chip, N6CA presented a power point presentation on the lay
out of the typical microwave transverter along with pictures of what
he was assembling for both himself and Paul, KH6HME in Hawaii. The
plan was to have a good low noise rig with several watts of transmit
power to over come the distance between Hawaii and the mainland
during the "Hawaii season" starting in July through the month of
August. The Produland 4 foot off set feed dish was already in place
atop the volcano in Hawaii. The feed is to be a W2IMU type design.